RFID systems are well suited to determining the location of vehicles. In such systems the vehicle may have a tag located therein where the vehicle passes readers at particular locations or it may have a reader located therein and there are tags at fixed locations. In systems of the latter type the tags may be embedded in the surface over which the vehicle travels. Systems of the latter type are generally preferred where the vehicle is traveling within a fixed and/or enclosed area.
In U.S. Pat. No. 6,049,745 a navigation system for an automatic guided vehicle is disclosed. Tags are embedded in a warehouse floor and a forklift having a reader located thereon is with use of the tags. In FIG. 1 of U.S. Pat. No. 6,049,745 tags are shown located along the centerline of the lane along which the forklift travels. It is further shown that the tags are more densely populated at the intersection of lanes allowing for realignment of the vehicle after a turn. With the use of a single tag along the centerline of a lane the disclosed system most readily provides for simple steering of the vehicle.
U.S. Pat. No. 6,377,888 discloses a system for controlling the movement of a vehicle that is free ranging within a defined area. In the disclosed system there are at least two RFID readers located in the vehicle and there is an array of tags embedded in the surface on which the vehicle travels. In one embodiment the tags are arranged such that only one of the tags is readable by a reader on the vehicle at any one time. It is further disclosed that a computer located in the vehicle receives location and acceleration data and calculates motion command signals for the vehicle. As disclosed between column 5, line 56 and column 6, line 12 the tags are of conventional construction.
U.S. Pat. No. 6,459,966 discloses a navigating method and device for an autonomous vehicle. An RFID reader is located on the vehicle and a row of tags is embedded in the floor. The reader has two antenna coils that are adjacent to one another and positioned left and right in the moving direction, column 6, lines 34-37. As shown in any of FIGS. 1-6 the beacons or tags are arranged in a single row. The trajectory of the vehicle is thereby determined by the positioning of the two antenna coils with respect to the row of tags.
The above systems are however not applicable to obtaining localization information for a freely traveling vehicle. In particular there is a need for determining localization information for a vehicle traveling along a track of limited width and be one of a plurality of adjacent tracks. In previous systems this problem was solved by scanning bar codes at the point of storage or by having the operator manually enter specific codes located on the floor.